There are currently various processes through which these effects are obtained on sheets having a front ply of plastics material suitably worked as a lens, behind which there are motifs which are viewed through said ply, providing the said effects.
Some of said processes are based on holographic reproduction, by engraving said reproduction on the rear surface of the plastics ply by heat and pressure and covering it with a reflective ply which allows the image to be viewed in 3-D through said plastics ply.
Other known processes are based on printing the motif to be viewed on a suitable sheetlike substrate, or directly on the rear surface of the plastics ply. The motif is printed with various stepped images or with multiple or offset photographs to obtain, through said ply, effects of images in different positions and/or depth after engraving striations or a reticule which forms optical lens on the front surface of the plastics ply.
With these processes and other known ones, sheets provided with the above effects are obtained, but they are of limited application due mainly to a thickness which makes them rather inflexible and which is a consequence of the nature of the said plastics ply.